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Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Manufacturing Processes Lab I MET 1321 Stick Welding part 2.

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Presentation on theme: "Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Manufacturing Processes Lab I MET 1321 Stick Welding part 2."— Presentation transcript:

1 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Manufacturing Processes Lab I MET 1321 Stick Welding part 2

2 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Electrodes Use the correct type of electrode for the welding to be done. Some electrodes can be used when welding with DC current, others are only used with AC current. If welding is to be done using DC current, determine whether DCEN or DCEP is needed for the particular electrode to be used. Select an electrode with a diameter that is about one- half the thickness of the metal to be welded. Use electrode until the stub is no longer than 1.5 to 2 inches.

3 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Electrode coatings Shielded electrode have coatings of various substances such as: Cellulose sodium, cellulose potassium, titan sodium, titania potassium, iron oxide, and iron powder, etc. Roles of the coating in the welding process: Acts as a cleaning and deoxidizing agent in the molten crater, Releases carbon dioxide to protect the molten metal from atmospheric oxides and nitrides (excludes oxygen and nitrogen because these contaminants weaken the weld), Forms a slag over the deposited metal that further protects the weld until the metal cools, Provides easier arc starting, stabilizes the arc and reduces the spatter, Permits better penetration and improves the X-ray quality of the weld.

4 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Identifying electrodes American Welding Society (AWS) classification: E H4 R E- identifies electrode for electric arc welding, 60- minimum allowable Tensile Strength in kips (thousands of pounds per square inch), eg: 60 shows the tensile strength of 60,000 psi. 1- indicates the possible welding location (1 means that electrode can be used for all positions, 2 for flat or horizontal ones only). 3- shows the special characteristics of the electrode, such as type of coating, weld quality, type of arc, or amount of penetration. H4- shows the hydrogen level. H4=hydrogen level less than 4 ml/100 g H8= hydrogen level of less than 8 ml/100g of electrode. R- indicates whether the electrode meets the requirements of the absorbed moisture test.

5 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Sticking an arc Set the polarity switch to the recommended position, Do not lay the electrode holder on the bench while current is flowing, Release the electrode if it sticks to the workpiece, Start with the recommended current range and adjust the current as necessary after welding begins, Always shut off the welding machine when leaving the welding bench.

6 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Sticking an arc Method 1: Method 2:

7 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Proper welding The arc length should be approximately the diameter of the electrode, Use the correct current for a particular electrode, Maintain a travel speed that is just fast enough to produce evenly spaced ripples. Short arc Sharp cracking sound Best for most welding Long arc Steady hiss allows Oxidation and spatter Setting the length of an arc

8 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Proper welding The depth of penetration should be 1/3 to 1/2 of the total thickness of the weld bead. Restart the electrode 1/2 inches from the front edge of the previously made crater, move the arc back through the crater to remelt the weld pool, and continue welding, When cleaning slag from the weld, using a chipping hammer or a wire brush, direct chipping away from the body, eyes and the face.

9 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Electrode angle

10 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Undercutting undercutting is a defect that appears as a groove along the edges of the weld. Undercutting is frequently just an appearance problem, but it can impair weld strength when the weld is loaded in tension or subjected to fatigue. To eliminate undercut: Reduce current and slow travel speed, or Change the electrode angle so the arc force holds the metal in the corners. Use a uniform travel speed and avoid excessive weaving.

11 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Welding parameters The current setting for any electrode diameter influences the fusion rate (deposition rate) and the penetration. The voltage varies with the arc length: - Long arc: higher voltage - Short arc: low voltage For direct current (DC), the correct polarity has to be chosen.

12 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Amperage If amperage is too high the following problems may arise: electrode may overheat, possibly damaging the flux coating oversize of the molten pool large crater at the end of weld with porosity and crack formation possible undercutting spattering slag hard to remove excessive penetration

13 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Amperage If amperage is too low the following problems may arise: difficulty in striking the arc discontinuous fusion of slag (flux coating) due to partial arc poor bonding and slag inclusions porosity

14 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Welding Speed If the welding speed is too high the following problems may arise: very narrow weld discontinuous fusion of slag incomplete fusion slag inclusions and porosity in the weld joints: insufficient penetration If the welding speed is too low the following problems may arise: wide weld slag inclusion in the weld joint, excessive penetration

15 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Arc Length If the arc is too short the following problem may arise: the arc chokes If the arc is too long the following problems may arise: the arc breaks porosities undercutting incomplete fusion spattering

16 Manufacturing Processes Lab 1 (MET 1321) Prof S. Nasseri Review the imperfections


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